PCI: tegra: Fix CLKREQ dependency programming

Corrects the programming to provide REFCLK to the downstream device
when there is no CLKREQ sideband signal routing present from root port
to the endpont.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thierry Reding <treding@nvidia.com>